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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 1386 (Engine Control System Diagnosis (DTC P0010 To DTC P0128) -- 1.8L (LV6)) >> Diagnosis >> DTC P0125 >> Test Description

Test Description

WARNING: This page is about a different car, the 2004 Pontiac Vibe. However, it is still accessible from the selected car via links, so may be relevant.

The numbers below refer to the step numbers on the diagnostic table.

  1. 1:  The Diagnostic System Check-Engine Controls prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.
  2. 3:  This step verifies whether the malfunction is a hard failure or an intermittent.
  3. 4:  This step verifies whether the PCM is able to receive a signal from the HO2S 1. The DMM is used as a low current voltage source taking the place of the HO2S.
  4. 8:  A condition that affects the fuel mixture or combustion event in the engine can impact the operation of the HO2S. This can cause an accurate signal from the HO2S to fail the diagnostic. Performing the tests listed in Diagnostic Aids will eliminate a faulty running condition and prevent the replacement of a good oxygen sensor.
DTC P0125

Step Action Values Yes No
Schematic Reference:  Engine Controls Schematics 
1  Did you perform the Diagnostic System Check-Engine Controls? - Go to Step 2  Go to Diagnostic System Check - Engine Controls
2
  1. Start the engine.
  2. Run the engine until the engine reaches a normal operating temperature.
  3. Select the HO2S 1 parameter on the scan tool.
  4. Snap the throttle.
  5. Observe the HO2S 1 parameter.
Does the HO2S 1 voltage vary within the specified range?		 200-900 mV Go to Step 3  Go to Step 4 
3 
  1. Perform the scan tool Clear DTC Information function.
  2. Place the vehicle into Check Mode, using the scan tool. Refer to Service Bay Test .
  3. Operate the vehicle within the Freeze Frame conditions as noted.
Does DTC P0125 set?		 - Go to Step 4  Go to Diagnostic Aids
4 
  1. Disconnect the HO2S 1 connector.
  2. Turn ON the ignition, with the engine OFF.
  3. Select the DMM to measure DC millivolts.
  4. Place the positive lead of the DMM on battery positive voltage, and the negative lead on the HO2S 1 input circuit terminal on the engine harness side.
  5. Observe the HO2S 1 voltage on the scan tool.
Is the voltage more than the specified value?		 1155 mV Go to Step 5  Go to Step 6 
5
  1. Connect a test lamp to battery voltage.
  2. Probe the HO2S 1 ground circuit terminal on the engine harness side.
Does the test lamp illuminate?		 - Go to Step 8  Go to Step 7 
6
  1. Check for an open or short in the HO2S 1 input circuit between the HO2S 1 and the PCM connector.
  2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.
Did you find and repair a condition?		 - Go to Step 11  Go to Step 10 
7 Repair the open in the HO2S 1 ground circuit between the HO2S 1 and G104. Refer to Wiring Repairs in Wiring Systems.
Did you complete the repair?		 - Go to Step 10  -
8 
  1. Before replacing the oxygen sensor inspect for the following conditions:
  2. Repair any condition found as necessary.
Did you find and repair a condition?		 - Go to Step 11  Go to Step 9 
9 Replace the HO2S 1. Refer to Heated Oxygen Sensor Replacement - Position 1 (FWD) or Heated Oxygen Sensor Replacement - Position 1 (AWD) .
Did you complete the replacement?		 - Go to Step 11  -
10 Replace the PCM. Refer to Powertrain Control Module (PCM) Replacement .
Did you complete the replacement?		 - Go to Step 11  -
11
  1. Use the scan tool in order to clear the DTCs.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.
Does the DTC run and pass?		 - Go to Step 12  Go to Step 2 
12 With a scan tool, observe the stored information, Capture Info.
Does the scan tool display any DTCs that you have not diagnosed?		 - Go to Diagnostic Trouble Code (DTC) List System OK
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